The effect of grain size and temperature on the superplastic deformation behavior of a 7075 Al alloy

Journal Article · Sun Aug 01 04:00:00 EDT 1999 · Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science

DOI:https://doi.org/10.1007/s11661-999-0014-z· OSTI ID:691376

Kwon, Y N; Chang, Y W ^[1]

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1. Pohang Univ. of Science and Technology (Korea, Republic of)

The high-temperature deformation behavior of a 7075 Al alloy has been investigated within the framework of a recently proposed internal-variable theory for structural superplasticity (SSP). The flow curves were obtained by performing a series of load relaxation tests for specimens with various grain sizes, at temperatures ranging from 445 C to 515 C. The overall flow curves were then separated into two parts, according to the respective physical mechanisms, viz., the grain-boundary sliding (GBS) and the accommodating dislocation glide processes, contrary to the conventional approach which uses a single power-law relation. These individual curves were then analyzed based on the internal-variable theory. Much valuable information has been obtained in this way, providing new physical insight as well as a more comprehensive understanding of SSP. The GBS curve could be described as a Newtonian viscous flow, signified by the power-index value of M{sub g} = 1.0 for this alloy. The unresolved issue of threshold stress is also clarified and identified as a critical stress required for the GBS. The role of grain refinement is found to shift the grain-matrix deformation (GMD) curve into a higher stress and strain-rate region, while the GBS curve into a lower stress and higher strain-rate region along the respective characteristic scaling line to bring both curves into a common flow-stress region, in which the GMD and GBS can operate simultaneously, resulting in the usual superplastic deformation behavior.

• Sponsoring Organization: USDOE
• OSTI ID: 691376
• Journal Information: Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, Journal Name: Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science Journal Issue: 8 Vol. 30; ISSN 1073-5623; ISSN MMTAEB
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM BASE ALLOYS
DATA ANALYSIS
DEFORMATION
FLOW STRESS
GRAIN REFINEMENT
GRAIN SIZE
PLASTICITY
TEMPERATURE RANGE 0400-1000 K